Multi-Functional Armor System

ABSTRACT

A ballistic armor adapted to protect against armor piercing projectiles and to withstand multiple impacts of fragment simulating projectiles of a predetermined type, traveling at an initial velocity not exceeding a first velocity. The armor comprises a main armor layer and an auxiliary layer. The main armor layer is adapted to absorb most of the energy of the armor piercing projectiles and to withstand the impacts of the fragment simulating projectiles traveling at a velocity not exceeding a second velocity which is lower than said first velocity. The auxiliary layer is disposed in front of the main armor layer to face the projectiles, and is made of a material which is adapted to undergo a ductile failure mode when perforated by said fragment simulating projectiles and thereby experience localized deformation in the vicinity of each perforation, and which is adapted to cause the fragment simulating projectiles to experience such an energy loss associated with the perforation and deformation as to reduce their velocity from the initial velocity to a velocity not exceeding the second velocity.

FIELD OF THE INVENTION

This invention relates to ballistic armor, particularly those suited to protect against fragmentation.

BACKGROUND OF THE INVENTION

When designing ballistic armor, for example, for protecting a vehicle, consideration must be given to the type or types of projectile against which the armor must protect. Some arrangements of armor will not protect at all against a certain type of projectile. For example, an array of ceramic tiles or pellets can protect against kinetic energy (KE) threats, such as direct hits of armor-piercing penetrators, while they generally do not provide protection against a plurality, i.e., hundreds, of fragments traveling at a high rate of speed as a consequence of an improvised explosive device (IED) exploding in the vicinity of an armored vehicle. Typically, the heavy fragmentation impacts resulting from the explosion of an IED destroy the hard, brittle ceramic, exposing the vehicle to be pierced by direct hit shots of sniper rifles or other similar threats.

When performing ballistic tests, it is not practical to explode an IED near an armor prototype. Therefore, fragment-simulating projectiles (FSPs) of different types are used. The impact of an FSP having a certain velocity on ballistic armor simulates the impact of a fragment resulting from an explosion of a known class of IED. Different size FSPs and their impact velocities correspond to different IEDs, such as mortars or artillery shells of a given diameter. By testing the armor prototype with an FSP, its ballistic capability against an IED threat can be determined.

An important consideration which must be taken into account when designing ballistic armor is the weight per coverage area of the armor. Theoretically, armor can be constructed to protect against almost any threat or combination of threats. On the other hand, the resulting weight of the armor needed for such protection has to be practical for the intended use, especially when the protection of vehicles such as trucks, armored infantry fighting vehicles, or armored personnel carriers, is concerned.

SUMMARY OF THE INVENTION

The present invention is directed to lightweight ballistic armor which can protect against both armor piercing projectiles and high speed fragments resulting from a nearby explosion of an IED or a high energy shell.

According to the present invention, there is provided a ballistic armor adapted to protect against armor piercing projectiles and to withstand multiple impacts of FSPs of a predetermined type, traveling at an initial velocity not exceeding a first specified velocity, and a method of such protection.

The armor comprises a main armor layer and a front auxiliary layer facing the projectiles, the main armor layer being adapted to absorb most of the energy of the armor piercing projectiles and to withstand the impacts of said FSPs when their velocity does not exceed a second velocity which is lower than the first specified velocity. The auxiliary layer is adapted for being perforated by said FSPs such the deformation of the auxiliary layer caused by its perforation by the FSPs is localized in the area of each perforation and the energy loss of the FSPs associated with the deformation and perforation gives rise to a reduction in velocity of the FSPs from their initial velocity to a velocity not exceeding the second velocity.

In order to be capable of the deformation as described above, the auxiliary layer is made of a material that, when perforated, undergoes ductile failure mode, also known as ductile exit. This mode as well as the associated perforation mechanism is described in detail in “Dynamic Perforation of Viscoplastic Plates by Rigid Projectiles” (M. Ravid & S. R. Bodner, International Journal of Engineering Science, Vol. 21, No. 6, pp 577-591, 1983) and “Penetration into Thick Targets—Redefinement of a 2D Dynamic Plasicity Approach” (M. Ravid & S. R. Bodner, International Journal of Impact Engineering, Vol. 15. No. 4, pp 491-499, 1994.

The material of which the auxiliary layer is made is further characterized in that it is of such hardness and thickness that sufficient energy of the FSPs is absorbed thereby to ensure the reduction in velocity of the FSPs from their initial velocity to a velocity not exceeding the second velocity. Experimental results show that this is obtained in materials whose the Brinell hardness is in the range of about 65 to about 165 kg_(f)/mm². Additionally, it is desirable that the material have an elongation greater than about 8%, and the yield strength in the range between about 11 and about 52 kg_(f)/mm² when tested at standard quasi-static test conditions.

Examples of materials having the above properties, and therefore suitable to be used for the auxiliary layer in the armor of the present invention, are aluminum alloys such as Al 6061, Al 7075, Al 2024, Al 5083, Al 7017, or Al 7019, and materials having similar properties.

Experiments show that the use of the auxiliary layer made of aluminum alloys as described above allows the armor to stop FSPs of diameters as large as 20 mm having velocities as high as 1500 m/s. This is a surprising effect, since aluminum is known to have relatively low ballistic protection capabilities when used as a frontal material, for which reason it is normally used in internal or backing layers. It is further surprising that commercial and common aeronautical alloys may be used successfully for ballistic protection as suggested in accordance with the present invention, though normally only special armor alloys are used for military applications. While there may be no significant weight difference between military and non-military aluminum alloys, the latter are normally less hard and are cheaper than the former.

The main armor layer may comprise a base layer made from a high density material of an appropriate thickness, such as high hardness steel and an additional, e.g., an add-on, layer. The latter may, for example, be of the kind comprising a plurality of tiles or pellets with or without a composite backing. The tiles or pellets may be made from, or comprise, metal (such as ultra high hardness steel) or a refractory or ceramic material such as alumina (Al₂O₃), silicon carbide (SiC), silicon nitride (Si₃N₄), or boron carbide (B₄C). The add-on layer typically is a frontal layer with respect to the base layer. The main armor layer may also be provided with an inner liner, which covers the base layer from behind. When the armor is designed to protect a vehicle, in particular its sidewall, the base layer may be constituted by said sidewall and the inner liner may be attached to the sidewall so as to protect the interior of the vehicle from shrapnel, and for absorbing remaining kinetic energy from armor piercing projectiles and fragments. The inner liner may be made from or comprise aramid materials, fiberglass, HDPE or laminated hybrids of such materials.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional side view of ballistic armor according to one embodiment of the present invention; and

FIG. 2 is a schematic cross-sectional side view of ballistic armor according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic representation of ballistic armor 10 according to one embodiment of the present invention, adapted to protect a vehicle (not shown) against both a fragment-simulating projectile (FSP) and an armor piercing projectile (APP) traveling in the direction indicated by arrow X.

The armor 10 comprises an auxiliary layer 12 and a main armor layer, which may or may not be separated by a gap 22, as shown in FIGS. 1 and 2.

The main armor layer 14 comprises a base layer 16, an add-on layer 18 and, optionally, an inner liner 20.

The base layer 16 is typically made from a hard metallic material such as RHA or high hardness steel which may have a thickness between 4 mm and 20 mm. In the present embodiment, this layer is constituted by the sidewall of the vehicle protected by the armor 10.

Alternatively, the base layer may comprise dual hardness armor (DHA). For example, such DHA may comprise a layer of UHH steel facing the projectile, and a layer of HH steel therebehind, the two layers being integrally attached to each other to form the base layer. The UHH layer may be thinner than the HH layer, e.g., its thickness may be about one third of the total thickness of the DHA, and the thickness of the HH layer may be two thirds thereof. With the base layer being made of DHA, the armor may provide an essentially enhanced ballistic protection.

The add-on layer 18 comprises an array of tiles or pellets 30, such as those composed of armor-grade alumina, another appropriate ceramic, or ultra high hardness steel. This layer may be constructed according to any one of a plethora of arrangements which are well known in the art and have an appropriate thickness for protection against armor piercing projectiles.

The inner liner 20 may be made from a composite laminate such as aramid, E-glass or S-glass fiberglass, high density polyethylene, or a hybrid thereof. This layer is attached to the inner side of the base layer 16, for example by gluing or bolting, as appropriate.

The add-on and base layers are adapted to absorb and dissipate kinetic energy of armor piercing projectiles and of FSPs, or residual fragments of improvised explosive devices, which will perforate the auxiliary layer 12, mainly due to the deformation and shattering thereof. The inner liner 20 is designed absorb remaining kinetic energy of, and to stop, any residual fragments which may pass the base layer.

The auxiliary layer 12 is made from a relatively soft ductile material, such as aluminum. The auxiliary layer 12 may be made from any material which experiences local deformation due to a ductile failure mode, as described in “Dynamic Perforation of Viscoplastic Plates by Rigid Projectiles” (M. Ravid & S. R. Bodner, International Journal of Engineering Science, Vol. 21, No. 6, pp 577-591, 1983) and “Penetration into Thick Targets—Redefinement of a 2D Dynamic Plasicity Approach” (M. Ravid & S. R. Bodner, International Journal of to Impact Engineering, Vol. 15. No. 4, pp 491-499, 1994), whose contents are incorporated herein by reference. As explained in the above articles, when material of the kind of which the auxiliary layer is made, is perforated by a projectile, the material's deformation during such perforation includes the stages of dynamic plastic penetration, bulge formation and bulge advancement stage at the end of which the projectile exists so that the exit lips at the rear surface of the material usually do not shear out. This leads to the material of the auxiliary layer being locally deformed at a plurality of locations upon its perforation by a plurality of FSPs, whereby multi-hit capability of the armor is ensured.

Additionally, the material has an elongation of greater than 8 percent, a yield strength not greater than 52 kg_(f)/mm², and a Brinell hardness not be greater than 165 kg_(f)/mm².

In operation, FSPs such as the FSP 24 which are typically between 0.3″ and 20 mm in diameter, and which travel at a high initial velocity, e.g., up to a first velocity of about 1500 m/s, pierce the auxiliary layer 12 in a plurality of separate locations, whereby a substantial portion of the kinetic energy of the FSPs is mitigated and their velocity is reduced to a second velocity within the range against which the main armor layer 14 can provide protection against the slowed down FSPs. The auxiliary layer 12 may also alter the trajectory and stability of the armor piercing projectiles so that they develops a yaw angle, which reduces their penetration capability. This effect is more pronounced in a case of oblique impacts of the armor piercing projectiles on the armor 10. In general, although armor piercing projectiles such as the APP 26, may also loose part of their kinetic energy when penetrating the auxiliary layer 12, this does not have to be the case since the main armor layer 14 may be adapted to protect against armor piercing projectiles without their previous energy absorption provided by the auxiliary layer 12.

In ballistic tests, different ballistic armors, each according to the present invention, were successfully tested against both FSPs and small caliber armor piercing projectiles at different velocities. All of the armors comprised auxiliary layers made of the same commercial aluminum alloy but having different thickness and base layers made of steel having different hardness and thickness. Some armors comprised an add-on ceramic layer made of cylindrical pellets held together by a thermoplastic or thermoset binder, the pellets being made of alumina (Al₂O₃ 98%), and having diameter 12.7 mm, and height 8 mm, and having domed front ends. Some of the armors comprised inner liner made of aramid and fiberglass. The test particulars are summarized in the table below.

TABLE 1 Multi-Functional Armor Test Parameters Main Armor Layer Inner Auxiliary Base Protective Layer Stand off Add-On Layer Layer Liner Projectile Velocity 15 mm Al 0 to — 10 mm 15 mm 20 mm FSP 1100 m/s 6061-T651 100 mm HHS Aramid and 7.62 × 54 mm API 830 m/s (42 kg/m²) Fiberglass B-32 16 mm Al 0 Ceramic layer (32 kg/m²) 10 mm — 20 mm FSP 1200 m/s 6061-T651 with fiberglass backing HHS 7.62 × 51 mm AP 950 m/s (44 kg/m²) FFV 16 mm Al 0 Ceramic layer (32 kg/m²) 10 mm 10 mm 20 mm FSP 1280 m/s 6061-T651 HHS Aramid and 7.62 × 51 mm AP 960 m/s (44 kg/m²) Fiberglass FFV ¼″ AL 0 to — 5.5 mm 15 mm 0.5″ FSP 1067 m/s 6061-T651 10 mm UHH Aramid and 7.62 × 54 mm LPS 866 m/s (17 kg/m²) Fiberglass HHS = High hardness steel (Armor type) UHH = Ultra high hardness (Armor steel)

Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis. 

1. Ballistic armor adapted to protect against armor piercing projectiles and to withstand multiple impacts of fragment simulating projectiles of a predetermined type, traveling at an initial velocity not exceeding a first velocity, the armor comprising: (a) a main armor layer designed to absorb most of the energy of the armor piercing projectiles and to withstand the impacts of said fragment simulating projectiles traveling at a velocity not exceeding a second velocity which is lower than said first velocity; and (b) an auxiliary layer disposed in front of the main armor layer to face the projectiles, the auxiliary layer being made of a material which is adapted to undergo a ductile failure mode when perforated by said fragment simulating projectiles and thereby experience localized deformation in the vicinity of each perforation; said auxiliary layer being adapted for being perforated by said fragment simulating projectiles such that an energy loss of the projectiles associated with said perforation and deformation gives rise to a reduction in their velocity from said initial velocity to a velocity not exceeding said second velocity.
 2. Ballistic armor according to claim 1, wherein the material of which the auxiliary layer is made is characterized in that its Brinell hardness is not greater than 165 kg_(f)/mm².
 3. Ballistic armor according to claim 1, wherein the material of which the auxiliary layer is made is characterized in that: (a) its elongation is greater than 8 percent; and (b) its yield strength is not greater than 52 kg_(f)/mm².
 4. Ballistic armor according to claim 1, wherein the auxiliary layer is made of an aluminum alloy.
 5. Ballistic armor according to claim 4, wherein the aluminum alloy is a selected from the group comprising aeronautical alloys and commercial alloys.
 6. Ballistic armor according to claim 1, wherein the auxiliary layer is spaced less than 100 mm from the main armor layer.
 7. Ballistic armor according to claim 1, wherein the auxiliary layer is in contact with the main armor layer.
 8. Ballistic armor according to claim 1, wherein the fragment simulating projectiles are up to 20 mm in diameter and said first velocity is 1500 m/s.
 9. Ballistic armor according to claim 1, wherein the main armor layer comprises a base layer made of a high density material.
 10. Ballistic armor according to claim 9, wherein the high density material is high hardness steel.
 11. Ballistic armor according to claim 10, adapted for mounting on a sidewall of a vehicle to protect at least one region thereof, wherein said base layer is at least partially constituted by said sidewall at said at least one region.
 12. Ballistic armor according to claim 1, wherein the main armor layer further comprises an additional layer.
 13. Ballistic armor according to claim 11, wherein the main armor layer further comprises an additional layer which is in the form of an add-on layer mounted to said sidewall at said at least one region.
 14. Ballistic armor according to claim 12, wherein the additional layer comprises a plurality of pellets or tiles held together by a binder material.
 15. Ballistic armor according to claim 14, wherein the pellets or tiles comprise a refractory material.
 16. Ballistic armor according to claim 14, wherein the pellets or tiles comprise ballistic ceramic.
 17. Ballistic armor according to claim 16, wherein the ceramic is selected from the group comprising alumina, silicon carbide, silicon nitride, and boron nitride.
 18. Ballistic armor according to claim 14, wherein the pellets or tiles are made of ultra high hardness steel.
 19. Ballistic armor according to claim 1, wherein the main armor layer further comprises an inner protective liner attached thereto on its side facing away from said auxiliary layer.
 20. Ballistic armor according to claim 19, wherein the inner protective liner is fiberglass.
 21. Ballistic armor according to claim 19, wherein the inner protective liner comprises aramid.
 22. Ballistic armor according to claim 19, wherein the inner protective liner comprises high density polyethylene.
 23. Ballistic armor according to claim 19, wherein the inner protective liner comprises a hybrid material.
 24. Ballistic armor according to claim 1, wherein the main armor layer comprises dual hardness armor.
 25. A method of ballistic protection against armor piercing projectiles and multiple impacts of fragment simulating projectiles of a predetermined type, each traveling at its initial velocity not exceeding a first velocity, method comprising: (a) providing a main armor layer adapted to absorb most of the energy of the armor piercing projectiles and to withstand the impacts of said fragment simulating projectiles traveling at a velocity not exceeding a second velocity which is lower than said first velocity; (b) providing an auxiliary layer made of a material which is adapted to undergo a ductile failure mode when perforated by said fragment simulating projectiles and thereby experience localized deformation in the vicinity of each perforation; and (c) disposing said auxiliary layer in front of said main armor layer so as to face the projectiles and to cause said fragment simulating projectiles to experiences such an energy loss associated with said perforation and deformation as to reduce their velocity from said initial velocity to a velocity not exceeding said second velocity. 